ray,

i have been sitting here trying to figure out how to really answer your question, and find that without doing a heck of a lot of research i cant.

i do know that if i look thru my information on tying soft hackles, most of my resources say the hackle should be about the length of the hook shank, and sparse. if i compare this information to soft hackles i see in the shops around here, the large percentage of them have hackle that is to long and to dense.

now whether this is a function of more appealing to the fish, or ease in tying the fly, i dont know. i do know that it takes a little more time and effort to get the correct hackle length and density.
i tie all my soft hackles sparse and with a hackle length just slightly longer than the fly body length and do quit well on the fish, would i do better with longer and more dense hackle, i dont know. i like the apperance of the shorter less dense hackled flies. these flies resemble in appearence the flies posted by our scottish freinds.

not sure this realyy answers your question, and its only my opinion.